Aroma compounds measurement methods

With methods in place to measure volatile aroma compounds within the olfactory space of individuals in real time, and to couple these to subjective reports of preference, it then becomes possible to combine these with more comprehensive measures of acute metabolism and physiology within an individual during the period when a novel food is being first perceived and olfactory preferences are being developed. 

F.1.2 Methods to Measure Interactions Between Aroma Compounds and Wine... 

The methods employed to measure the interactions that occur between aroma compounds and other food or beverage constituents are frequently based on measuring changes in the vapour-liquid equilibrium when different macromolecules are present in the media. The determination of the gas-liquid partitioning with and without a food macromolecule is widely employed. 

Some static headspace methods do not require an external calibration and are based on measurements performed at thermodynamic equilibrium between liquid and gas phase. In the phase ratio variation method (PRV) described by Ettre and Collaborators (1993), the partition coefficient calculation is based on the fact that the headspace concentration changes as a function of the phase volume ratio (gas and liquid phases), while the partition coefficient remains constant. This method has been recently applied to study the interactions between aroma compounds and macromolecules in different food systems (Savary et al. 2006, 2007) but so far not to the wine. 

Other methods to determine the interactions between aroma compounds and wine matrix components do not involve gas phase measurements. For example, the equilibrium dialysis method has been applied for determining interactions between yeast macromolecules and some wine aroma compounds (Lubbers et al. 1994a) and more recently to study the interaction of aroma compounds and catequins in aqueous solution (Jung and Ebeler 2003). While this method can be set up in different ways, a simple approach is to fill a dialysis cell (two chambers separated by a semiper-meable membrane) with an aromatized liquid. A non-volatile component of wine can be added to one chamber of the cell and then the system allowed to come to equilibrium. If the added non-volatile component binds the aroma compound, the other chamber will be depleted by this binding. Quantification of this change in concentration permits calculating the quantity that is bound to the added substrate. 

Athes, V, Lillo, M.P.Y., Bernard, C., Perez-Correa, R., Souchon 1. (2004). Comparison of experimental methods for measuring infinite dilution volatilities of aroma compounds in water/ethanol mixtures J. Agric. Food Chem, 52, 2021-2027. 

As has been previously said, 2,3-butanodione (diacetyl) is an important aroma of alcoholic beverages, it has not been studied and measured extensively in the past because of analytical difficulties in the quantitation caused by its highly volatile nature, chemical instability, and interference of other compounds. Colorimetric methods to measure diacetyl have been widely used in the past. These methods involve steam distillation to isolate diacetyl from the matrix. However, distillation has the disadvantage of incomplete isolation of diacetyl from other closely related compounds that will result in an overestimation of its concentration. A fluorometric method was developed to improve upon the lengthy distillation methods that involve derivatization. Although acetaldehyde and its acetal can be determined by direct injection GC-FID in spirit drinks (EU reference method for spirits), most chromatographic methods for minor aldehydes implicate also derivatization. While a very sensitive and accurate method based on SMPE without derivatization and MS detection has been developed, it requires the use of... 

Literature and knowledge on mass transfer of aroma compounds are few and no standard procedure is recommended. Methods developed for aroma compounds permeability measurements are commonly approached by isostatic or quasiisostatic methods and depend on the physical state (vapor or liquid) of the aroma compounds (Piringer and Baner 2000). 

This chapter will discuss the basis of the methods used in the isolation and analysis of food aroma components. It will be pointed out repeatedly that there is no single method of isolation or analysis that provides a complete view of the aroma compounds found in a food. The goal is to find an analytical method that can measure those components that are of interest to the analyst. They may be, for example, the compounds that give an off-flavor or those that give a fresh note to a food. Unfortunately, any aroma profile will be a partial view of the overall picture. The reader is encouraged to obtain a more complete discussion of this topic than can be provided in this text and suggests references [5-8] as sources. 

Our interest in the analysis of nonvolatiles, thus, may involve taste substances or substances that indirectly influence taste or aroma. As mentioned earlier, in the first case, we are interested in the analysis of substances that impart sweetness, tartness, bitterness, saltiness, or unmami sensations. The analysis of these substances is reasonably well defined. In the latter case, the analyses employed are less well defined and are unique to the components one wishes to analyze. For example, we may wish to measure substances (e.g., melanoidins) that interact with sulfur aroma compounds (in coffee). There are no standardized methods for the analysis of melanoidins in foods and thus, the protocols have to be developed. In this chapter, we will only briefly discuss the established methods for the analysis of taste substances. Due to the specificity of methods for the analysis of nonvolatiles that may indirectly influence flavor perception, we will only refer the reader to the literature [93-100]. 

Studies on starch demonstrate that starch will include aroma compounds the extent of inclusion will depend upon the starch (proportion of amylose to amylopectin), its processing history, and the aroma compound. Hau et al. [19] have presented a view of the extent of interactions one observes via static methods (measure of chemical interactions) between selected aroma compounds and starch (Figure 6.6). It is clear that the amount of interaction is quite significant for some compounds (nearly 80% of the hexanol is bound). The interaction is both compound and time dependent (although most compounds reached a plateau in binding after only 1 hr). It is postulated that free amylose forms a helical structure that has hydrophobic areas that will include certain aroma compounds. It should be noted that this research... 

Charm analysis constructs chromatographic peaks, the areas of which are proportional to the amount of the odorant in the aroma concentrate [4], The difference between the two methods is that charm analysis measures the dilution value over the entire time the compounds elute, whereas AEDA simply determines the maximum dilution value [8],... 

Since 1985, the methodology discussed in the preceding sections has been applied to the aroma analysis of a large number of foods. The compounds which were identified and their concentrations, as far as measured with a precise method like SIDA, are discussed in the following section. Additionally, as they are of potential commercial interest, the OAVs are listed in the tables. 

Characteristic aroma components in foods and off-flavor substances in processed foods are called character impact compounds. It would be desirable to develop methods for finding such compounds with sensory methods because such information is useful in the food industry. A compilation of odor and taste threshold values was edited by Fazzalari (7). Olfactory-trigeminal response to odorants was measured using rabbits (2). However, aroma quality can be evaluated only by human sense. In spite of this fact, olfactory judgment by humans can not give constant data like... 

In AEDA, the assessor indicates whether or not an aroma can be perceived and notes the sensory descriptor. The result is expressed as the flavor dilution (ED) factor that corresponds to the maximum dilution value detected, i.e., the peak height obtained in CharmAnalysis. The FD factor is a relative measure and represents the odor threshold of the compound at a given concentration. The data are presented in an FD chromatogram (Fig. 5) indicating the retention indices (x-axis) and FD factors in a logarithmic scale (y-axis). AEDA has been proposed as a screening method for potent odorants as the results are not corrected for losses during isolation (7). 

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